A Constitutive Cdm Model and Its Application to Grinding Damage Prediction for Ceramics

Grinding can introduce surface and subsurface damage into ceramics, which may reduce the load-bearing area, and thus the residual strength of a ground component. In this study, the principle of continuum damage mechanics (CDM) is applied to predicting grinding damage for ceramics. A nonlinear thermodynamic constitutive model is established to describe the response of ceramics to complex grinding loading. The model consists of a series of Maxwell-type elements arranged in parallel together with a spring in series. It incorporates stochastic material microstructure through two sets of the newly introduced material parameters, spring constants Cr and damping-like coefficients ar (r=1, 2, ..., n). Damage is considered cumulative in a ceramic workpiece during grinding, which constitutes damage evolution. In constructing the equation for damage evolution, considered are the current state of effective stress and damage, the effect of hydrostatic stress and the coupling effect between the hydrostatic and deviatoric stresses. A fourth-order isotropic damage tensor is introduced. A three-dimensional finite element program is developed to facilitate damage prediction for alumina, silicon carbide, and silicon nitride subjected to single-grit grinding. A moving sinusoidally distributed load is used to simulate the loading condition in single-grit grinding. The results show that the damage is mainly induced by von Mises equivalent stress, i.e., the shear stress, rather than the hydrostatic stress in the ground workpieces. The model is validated by the experimental results.